U.S. Pat. No. 3,714,879 describes a single lens reflex camera which folds into a thin, compact configuration suited for carrying in the pocket of a garment. The camera is particularly characterized by its fully automatic operation. In using it, an operator views and focuses a scene to be photographed, following which a start button is lightly and only momentarily touched to cause the camera to automatically carry out a photographic cycle. This cycle includes such operational events as the securing of the exposure plane of the camera while the components thereof alter to define an exposure mode optical path. Actuation of the components to commence such path alteration is initiated by the momentary energization of an electric motor. Following such momentary energization, spring biased components carry out the noted optical path manipulation. This operation of the camera is described in U.S. Pat. No. 3,731,608. Following the development of an exposure mode orientation of the components of the camera, a light sensitive circuit therewithin regulates an exposure mechanism to define a value of exposure in accordance with scene brightness.
At the conclusion of an exposure interval, the exposure plane of the camera again is secured as the motor is energized to alter the components thereof to the initial viewing and focusing mode orientations. Simultaneously, the exposed film unit within the camera is driven through a processing station and removed from the camera for development externally thereof.
Where flash illumination is utilized in conjunction with the camera, the same operational cycle is carried out with the exception of alterations in the form of automated exposure control.
Another feature of the camera is provided in conjunction with the initial insertion of a package or cassette of film therewithin. As described in U.S. Pat. No. 3,750,551, when the film cassette is inserted within the camera and the accessing components of the camera are returned to a secured position, the uppermost dark slide component of the cassette automatically is driven from the camera.
The automatic exposure system retains the capability for carrying out time exposures extending beyond intervals of exposure suited for hand-held performance. For instance, exposures automatically may be regulated for intervals extending up to about 20 seconds. An inexperienced operator may be unaware that steady or secure camera support is needed for low light level performance or that artificial or flash illumination should be utilized under a given low light level condition. Accordingly, a technique for apprising the operator of low scene light level conditions would be helpful. However, inasmuch as a camera such as the automatic one described above is committed to the carrying out of a full cycle upon momentary depression of a start button, mere warning techniques, without more, are of marginal value. An arrangement for automatically blocking the carrying out of a photographic cycle under low light level conditions has some value. However, extended exposure interval or time exposure photography then would not be available. Lack of such a capability in a photographic device is highly undesirable. Further, where such cameras incorporate the above-noted automatic dark slide ejection feature, such feature may be hindered where film loading takes place in low light level environments.